Rotary drum type continuous refining furnace

ABSTRACT

Disclosed is a rotary drum type continuous refining furnace including a discharging trough presenting a scoop portion for scooping molten metal from the chamber of the furnace and depositing the same in the furnace outlet whereby the amount of residual molten metal remaining in the refining furnace after the completion of the refining operation is minimized. Further, the internal chamber of the furnace is provided with a non-circular cross-sectional configuration in a plane extending perpendicularly of the longitudinal axis thereof for the purpose of improving the mixing action in the chamber during the operation of the furnace.

[111 3,743,265 .July 3 1973 United States Patent [191 Tanoue et al. 7 u

[ ROTARY DRUM TYPE CONTINUOUS REFINING FURNACE 7 Primary Exqmjner -Gerald Dost [75] Inventors: Toyosuke Tanoue, Toyonaka; AnQmeyT'watSon Cole Grmdl'e & Watson Kyoichi Akamatsu, Ibaragi,

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BY Mai s, iywlll ATTORNEYS ROTARY DRUM TYPE CONTINUOUS REFINING FURNACE This invention relates to the field of rotary drum type continuous refining furnaces and particularly to improvements for such furnaces wherein the efficiency of the mixing operation is increased and the removal of molten metal from the furnace at the completion of the refining operation is enhanced.

Conventional rotary drum type continuous refining furnaces, for example, rotary drum furnaces used for the continuous desulfurization of molten pig iron, generally include a cylindrical furnace body having an internal chamber which has a circular cross-sectional configuration. The furnace body is mounted in a position with its longitudinal axis slightly inclined from the horizontal and molten metal and the refining agent are continuously poured thereinto' through an inlet port at the most elevated end thereof. The molten metal and the refining agent are agitated and mixed in the furnace body which is rotated about its longitudinal axis for the purpose of accelerating the refining reaction. When the refining reaction is complete, the molten metal and the refining agent residue are continuously removed from the furnace through a discharging port disposed at the opposite end of the furnace from the inlet port.

In such a metal refining process, in order that the refining reaction may reach theappropriate level, it is desirable to provide adequate mixing by rotation of the furnace coupled with a sufficient residence time to permit the occurrence of a complete reaction of the ingre dients.

In a conventional furnace having a circular crosssectional configuration, the amount of molten metal within the furnace body must be increased if a corresponding increase in the residence time of the metal is desired. An increase in the amount of metal will necesaxis of the furnace body for the purpose of increasing the efficiencyof the mixing action in the furnace during its operation. Inlet port means are provided at one end of the furnace body for facilitating the continuous pouring of molten metal into the chamber. Outlet port means are provided at the other end of the furnace body and generally at the axis of rotation thereof for continuously discharging molten metal products from the chamber. Also included are wall means disposed between the chamber and the outlet port means presenting a discharging trough extending along the axis of rotation of the furnace for intercommunicating the internal chamber of the furnace and the outlet port. The discharging trough includes a semicircular portion disposed at theaxis of rotation of the furnace and a scoop portion extending'outwardly from said axis at least as far as the adjacent,.corresponding internal surface of the chamber, for scooping molten metal from the chamber and depositing the same in the outlet port means as the furnace body is rotated. The crosssectionalconfiguration of the internal chamber of the furnace may be in the shape of a drum, in the shape of an ellipse, in the shape of a regular polygon or in the furnace in order to obtain the mixing action requisite to a complete refining reaction. Such an increase in the rotational speed of the furnace will result in a corresponding increase in the wear and tear to which the rotating device is subjected and therefore an increase in operational and capital expenditures.

Further, with conventional rotary drum type furnaces, the process of removing molten metal unavoidably remaining within the furnace at the end of the operation is troublesome and complicated equipment has generally been believed requisite.

An object of the present invention is to provide a rotary drum type continuous refining furnace wherein the foregoing defects are eliminated. In accordance with the invention, a furnace is provided wherein agitation action and residence time are sufficient even with a low rotational speed and wherein metal which remains in chamber. The furnace body is adapted for subjecting molten metals in the chamber to a refining reaction. Included are means mounting the furnace body for rotation about its longitudinal axis and the chamber is provided with a non-circular cross-sectional configuration in a plane extending perpendicularly of the longitudinal shape of a circle having inwardly extending projections.

In the drawings: FIG. 1 is a partly exploded perspective view of a rotary furnace embodying the'concepts and principles of the present invention;

, trating another embodiment of the invention wherein a dam is provided between the inside of the furnace and the discharging trough; i

FIG. 7 is a cross-sectional view similar to FIG. 3 illustrating still another embodiment of the invention wherein a section of the scoop portion of the outlet trough of the furnace is stepped radially outwardly of the internal chamber thereof;

FIG. 8 is a cross-sectional, side elevational view of an embodiment of the invention wherein both the dam of FIG. 6 and the step section of FIG. 7 are provided;

FIG. 9 is a cross-sectional view taken substantially along line IX-IX of FIG. 8;

FIGS. 10a through 10h are views illustrating the sequential operation of the furnace;

FIG. 11 is a diagram showing the relationship between the length of the discharging trough and the time required for completely discharging the furnace; and

FIGS. 12 and 13 are diagrams showing the sulfur content-of the discharging molten pig iron and the variation of temperature, respectively, with elapsed time after the beginning of a continuous desulfurization operation.

A rotary drum type furnace constructed in accordance with the principles and concepts of the present invention for continuously refining molten metals, is

illustrated in the drawings. As is shown in FIGS. 1

through 4, the furnace includes an elongated, hollow,

cylindrical furnace body 1 which has an internal chamber having a drum-shaped cross-sectional configuration in a plane extending perpendicularly of the longitudinal axis of body 1.

Body I is mounted for rotation on two sets of wheels 4 provided on opposite sides of a rotation driving stand 3, as is illustrated in FIGS. 1 and 4. Stand 3 is mounted on the upper inclined surface of an inclined base 2. The wheels 4 of each set thereof are interconnected by an axle 5 and at least one of the axles 5 is connected to the main shaft of an electric motor (not illustrated), through a reduction gear, so that the torque of the electric motor may be transmitted to the furnace body 1 for the purpose of rotating the latter. An inlet port 6 for facilitating pouring of molten metal and a refining agent (which may be an alloying agent) into the furnace body, is provided at the more elevated end of the furnace body 1, and a discharging port 7, which is concentric with the axis of rotation of body I, is provided at the lower end thereof.

A discharging trough 8 is provided between the interior of body 1 and outlet port 7. Trough 8 includes a wall which extends tangentially relative to one side of an arcuate portion 9 of trough 8. Arcuate portion 9 is presented by a semicircular, axial extension of the interior peripheral surface of discharging outlet port 7. Trough 8 also includes a wall 11 which extends in a direction radially of the center of portion 9. Walls 10 and 11 are interconnected at their ends remote from said portion 9 by a circumferentially extending wall 12 formed as an extension of the interior peripheral wall of furnace body 1. Trough 8 opens into the interior of furnace body 1 at 13 and the peripheral edges of the walls presenting trough 8 are connected to furnace body 1 by an end wall 14 of the furnace body. An outside wall 15 is formed around discharging outlet port 7. Together, walls 10, 11 and 12 present a scoop portion of trough 9 which communicates with semicircular portion 8 which in turn communicates with discharging outlet port 7.

As shown in FIG. 4, the cross-sectional configuration of the internal chamber of the furnace body, in a plane extending perpendicularly of the axis of rotation thereof, is in the shape of a drum. However, it should be appreciated that this chamber may have any noncircular shape, such as that of an ellipse, that presented by a combination of straight lines such as a regular polygon, that presented by a combination of curved lines or a combination of straight lines and curved lines, or that presented by a circle provided with projections or baffles on its inner periphery.

Further, while the cross-sectional shape of discharging trough 8 is preferably as shown in FIG. 3, the same may be configured in other shapes, such as, for example, (a) a shape formed by extending the sides of the scoop portion of discharging trough 8 reversely of one another in a direction tangentially of portion 8 (FIG. 5a); (b) a shape formed by extending the sides of said scoop portion reversely of one another in a direction radially of portion 9 (FIG. 5b); (0) a shape formed by extending the sides of the scoop portion in a direction tangentially of portion 9 in the same direction (FIG. 5c).

In order to more efficiently completely discharge residual molten metal from the furnace after treatment thereof has been completed, a dam 16 may be provided at the internal end of portion 9 of discharge trough 8 as shown in FIG. 6. Additionally, a peripheral wall 12 may be positioned as shown in FIG. 7 to present a section 19 of the scoop portion which is stepped radially outwardly of the interior chamber of the furnace. If both a dam 17 and a stepped section 19 are provided, as shown in FIGS. 8 and 9, even more efficient results may be obtained.

During the operation of the rotary drum type continuous refining furnace of the present invention, molten metal and a refining agent (which may be an alloying agent) are continuously poured into furnace body 1 through inlet port 6 while furnace body 1 is rotated. Thus, the metal and refining agent are mixed and agitated within the furnace and a sufficient residence time is provided to permit the completion of the refining reaction; Then, the refined molten metal is continuously discharged from furnace body 1 through outlet port 7 by virtue of the scooping discharging action of the scooping portion of discharging trough 8 during the to tation of furnace body 1. Thus, the continuous refining treatment is continued until the charging of ingredients through inlet port 6 is discontinued.

After charging of ingredients through port 6 is discontinued, the interior of the furnace will be emptied by the action of trough 8 as illustrated in FIGS. 10a through 10h. Thus, molten metal and refining agent residue remaining within the interior of furnace body 1 will be completely scooped up into the state shown in FIG. 10f, by rotation of trough 8 in the direction indicated by the arrow in FIG. 10a, through the states shown in FIGS. 10a through l0e. Thereafter, the molten metal will flow out to discharging port 7 through discharging trough 9,-as shown in FIG. 10g, and will be completely discharged, as shown in FIG. 10h. Accordingly, with each complete rotation of furnace body 1, a separate scooping discharge will be made and as the furnace body continues to rotate, all residual molten metal and refining agent will be completely discharged from furnace body 1.

The relationship between the cross-sectional configuration of the interior of the furnace in a plane extending perpendicularly of its longitudinal axis and the shape of trough 9, during the operation of the furnace, are described below in detail. In a rotary drum type furnace, if the rotational speed of the furnace body is within a predetermined range, a vigorous rainfall-shaped agitation action will occur to efficiently mix the ingredients in a preferred manner. As the rotational speed is increased beyond the upper level of the range, the rainfall-shaped agitation action will stop and the crosssectional shape of the contents within the furnace will become annular. Thus, the contents of the furnace will tend to rotate with the furnace without being properly mixed. Accordingly, only when the rotational speed is within a specific range, will the preferred rainfallshaped agitation action occur.

The rotational speed range required to provide the preferred action varies with the shape and dimensions of the interior chamber of the furnace, and with the amount of the molten metal therewithin. However, in accordance with the present invention, it has been found, as is shown in Table I, that severe rainfallshaped agitation action may be caused to occur at a lower rotational speed when the cross-sectional configuration of the interior of the furnace, in a plane extending perpendicularly to the longitudinal axis of the furnace, is non-circular, such as, for example, drumshaped, elliptical, polygonal, or circular but provided with an interior baffles or projections. Moreover, in an apparatus which embodies the principles and concepts of the present invention, a rotational speed corresponding to a centrifugal force of less than 12.0 G, (based on the longest diameter in the interior of the furnace) .produces the same rainfall-shaped agitation action as is obtained through the use of an ordinary circular crosssection only with a rotational speed which corresponds to a centrifugal force of more than 17.2 G. In the experiments conducted to produce the data for Table l, the molten metal occupied 25 to 30 percent of the internal volume of the furnace. Under these conditions, a sufficient residence time for the occurrence of the refining reaction was provided.

TABLE I Proper value to obtain rainfall-shaped agitation action Cross-sectional configuration of the interior of the furnace in a plane extending per- Rotational Centrifugalpendicularly of the longitudinal axis speed force thereof (r.p.m.) number) glllicle (8%) mm. in diameter) 195-300 17. 2 10.2 ipse 00 min. in major ax Ratio 01 major axis/minor axis Polygon (800 mm. in the maximum diagonal length):

Regular octagon 162-208 11. 7-10. Regular hexagon 137-208 8. 5-10. Circle with baffles (4 balfies. 800

mm. in diameter): Ratio of bafl'ic 0.025 126-170 7. 213. height/circle diameter 0. 050 68-137 2.1- ii. U. 075 56403 1.4 4. Drum shape: Ratio, of long diameter/short diameter. 1. 21 58-125 1.5- 7.1

With regard to the discharge of molten metal remaining in the furnace after the refining treatment, the relationship between the shape of the discharging trough and the rotational characteristics of the furnace body has been investigated. The results of this investigation are set forth in Table 11. With any of the discharging trough shapes shown in FIGS. 3, 5a, 5b and 5c, the maximum discharging rate was obtained with a rotational speed lower than that necessary during continuous refining treatment. The maximum discharging rate was generally obtained, with any of the illustrated discharging trough shapes, when the centrifugal force due to the rotation was about 1 G.

in furnaces constructed in accordance with FIGS. 6, 7 and 9, wherein a stepped section is provided in the discharging trough, the time required for complete discharge is plotted, in FIG. 11, against the ratio of the axial length of the discharging trough to the axial length of the interior of the furnace body. in FIG. 11., curve (a) represents the results of experiments conducted to determine the'time required for complete discharge with a discharging trough having no dam or stepped section (FIGS. 1, 2 and 3); curve (b) represents tests conducted with a discharging trough provided with a stepped section of mm. but no dam (FIG. 7'); curve (c) represents tests conducted with a discharging trough having a dam but no stepped section (FIG. 6); and curve (d) represents test conducted with a trough having a dam and a stepped section of 50mm (FIGS. 8 and 9).'As can be seen in FIG. 11, as the length of the discharging trough increases relative to the length of the interior of the furnace body, the discharge time for the molten metal becomes shorter. Further, it can also be seen that the discharging efficiency of a discharging trough provided with a stepped section or a dam or with both of them is greater than that of a trough provided with neither.

Specific examples of the operation of furnaces embodying the concepts and principles of the present invention are set forth below:

EXAMPLE .I

Molten pig iron was continuously desulfurized in a rotary drum type refining furnace at the following operating conditions and characteristics:

MAIN DIMENSIONS OF THE FURNACE BODY:

Shape and dimensions of the cross-sectional configuration of the interior of the furnace body: Drum-shape having relative dimensions as shown in FIG. 3.

Length of the interior of the furnace body: 3300 mm (as shown in FIG. 2).

Length of the discharging trough: 240 mm (as shown in FIG. 2).

Dimensions of the inlet port: 330 mm in diameter and 500 mm long (as shown in F168. 2 and 4).

Dimensions of the semicircular portion of the discharging trough: 180 mm in diameter (as shown in MG.

TABLE II Centrifugal iorce (G Furnace number) total amount discharged (kg) body due to rotational rotation Time elapsing alter the beginning of rotation Shape of discharging speed of furnace part (r.p.n1.) body 20 see. 40 see. see. 100 see. 140 see. 180 see.

Fig. 24 0.25 1,100 1,810 2,100 2,250 2, 270 1 35 0. 55 1,730 2, 210 2, 240 2, 250 l A 00 2. 15 820 l, 210 l, 420 1,000 1,080 l, 720

Fig. 6(a). 24 0. 25 1,210 1, 820 2,120 2, 250 2, 270

Fig. 5(1)) 24 0. 25 800 1,200 1, 100 1, 830 2, 000 2, 200

69 2. 15 030 1,010 l, 310 1, 050 l, 700 1, H40

Fig. 5(a) 24 0. 25 800 1,450 1, 800 2, 200 2, 220 2, 230

N0'ri"..--Ihe mark shows complete discharge.

Dimensions of the outlet port: 180 mm in diameter and 300 mm long (as shown in FIG. 2).

Angle of inclination: 3.

ROTATING CONDITIONS: Centrifugal force: 6 G. Rotational speed: 115 r.p.m.

The sulfur content of the discharged molten pig iron and the variation of temperature with elapsed time after the beginning of the continuous desulfurizing treatment, are shown in FIGS. 12 and 13. As can be seen, a low sulfur content pig'iron containing 0.004 to 0.006% S is continuously produced and the temperature dropin the molten pig iron at steady state conditions is only about 10 to 20 C.

EXAMPLE ll:

Discharge efficiency experiments were made by providing discharging troughs having shapes as whown in FIGS. 3, 5a,'Sb and 5c. These troughs were utilized in combination with a furnace body having a drumshaped internal cross-sectional configuration as shown in FIG. 4. All other conditions were as set forth in connection with Example 1. After the introduction of molten pig iron into the furnace had been discontinued and after the discharge of molten pig iron from the discharging outlet port had substantially stopped, the rotational speed of the furnace body was reduced from 115 rpm. (6 G) down to 45 rpm. (0.9 G) and the residual molten pig iron was discharged by the scooping action of the discharging trough. The results of these experiments are shown in Table IV.

TABLE IV Cross-sectional shape of the discharging trough Tune for complete discharge of molten pig iron 1 minute 52 seconds 1 minute 50 seconds 3 minutes 2 minutes 20 seconds Shown in FIG. 3 Shown in FIG. 5a Shown in FIG. Sb Shown in FIG. 5c

cross-sectional configuration in a plane extending perpendicularly of said axis;

inlet port means at one end of the furnace body for facilitating the continuous pouring of molten metal into said chamber;

outlet port means disposed at the other end of the furnace body and generally at said axis for continuously discharging molten metal product from said chamber; and

wall means disposed between said chamber and said outlet port means presenting a discharging trough extending along the axis and intercommunicating the chamber and the outlet port,

said trough including a semicircular portion disposed at said axis and a scoop portion extending outwardly from the axis at least as far as an adjacent, corresponding internal surface of the chamber, for scooping molten metal from the chamber and depositing the same in said outlet port means as the furnace body is rotated.

2. A drum type furnace as set forth in claim 1 wherein said cross-sectional configuration of the chamber is in the shape of a drum.

3. A drum type furnace as set forth in claim 1 wherein said cross-sectional configuration of the chamber is in the shape of an ellipse.

4. A drum type furnace as set forth in claim 1 wherein said cross-sectional configuration of the chamber is in the shape of a regular polygon.

5. A drum type furnace as set forth in claim 1 wherein said cross-sectional configuration of the chamber is in the shape of a circle having inwardly extending projections.

6. A drum type furnace as set forth in claim 1 wherein a dam is provided between said chamber and said semi-circular portion of the trough.

7. A drum type furnace as set forth in claim 1 wherein said scoop portion of the trough extends outwardly beyond said adjacent internal surface presenting a section of the scoop portion which is stepped radially outwardly of the chamber.

8. A- drum type 'fumace as set forth in claim 7 wherein a dam is provided between said chamber and said semi-circular portion of the trough.

9. A drum type furnace as set forth in claim 1 wherein said scoop portion of the trough is formed by at least one wall extending tangentially of said semicircular portion.

10. A drum type furnace. as set forth in claim 1 wherein said scoop portion of the trough is formed by at least one wall extending radially of the center of said semi-circular portion.

11. A drum type furnace as set forth in claim 10 wherein said scoop portion of the trough is formed by at least one wall extending tangentially of said semicircular portion.

12. A drum type furnace as set forth in claim 1 wherein said scoop portion of the trough is formed by at least two walls, each extending tangentially of said semicircular portion.

13. A drum type furnace as set forth in claim 12 wherein the walls forming the scoop portion of the trough extend in the same direction away from the semicircular portion.

14. A drum type furnace as set forth in claim 12 wherein the walls forming the scoop portion of the trough extend in opposite directions away from the semicircular portion. 

2. A drum type furnace as set forth in claim 1 wherein said cross-sectional configuration of the chamber is in the shape of a drum.
 3. A drum type furnace as set forth in claim 1 wherein said cross-sectional configuration of the chamber is in the shape of an ellipse.
 4. A drum type furnace as set forth in claim 1 wherein said cross-sectional configuration of the chamber is in the shape of a regular polygon.
 5. A drum type furnace as set forth in claim 1 wherein said cross-sectional configuration of the chamber is in the shape of a circle having inwardly extending projections.
 6. A drum type furnace as set forth in claim 1 wherein a dam is provided between said chamber and said semi-circular portion of the trough.
 7. A drum type furnace as set forth in claim 1 wherein said scoop portion of the trough extends outwardly beyond said adjacent internal surface presenting a section of the scoop portion which is stepped radially outwardly of the chamber.
 8. A drum type furnace as set forth in claim 7 wherein a dam is provided between said chamber and said semi-circular portion of the trough.
 9. A drum type furnace as set forth in claim 1 wherein said scoop portion of the trough is formed by at least one wall extending tangentially of said semicircular portion.
 10. A drum type furnace as set forth in claim 1 wherein said scoop portion of the trough is formed by at least one wall extending radially of tHe center of said semi-circular portion.
 11. A drum type furnace as set forth in claim 10 wherein said scoop portion of the trough is formed by at least one wall extending tangentially of said semicircular portion.
 12. A drum type furnace as set forth in claim 1 wherein said scoop portion of the trough is formed by at least two walls, each extending tangentially of said semicircular portion.
 13. A drum type furnace as set forth in claim 12 wherein the walls forming the scoop portion of the trough extend in the same direction away from the semicircular portion.
 14. A drum type furnace as set forth in claim 12 wherein the walls forming the scoop portion of the trough extend in opposite directions away from the semicircular portion. 